Synthesis, Characterization, and Application of Ultrasmall Nanoparticles

Nanomaterials in the size range of 3–50 nm have received increased attention in the last few decades because they exhibit physical properties that are intermediate to those of individual molecules and bulk materials. Similarly, ultrasmall nanoparticles (USNPs), with sizes in the 1–3 nm range, exhibit unique properties distinct from those of free molecules and larger-sized nanoparticles. These properties are greatly sensitive to both the composition and size of the particles, and thus, the ability to control the synthesis for both of these variables is of paramount importance. This review summarizes various methods for the synthesis of USNPs of metals, metal oxides, and metal chalcogenides as well as recent advances in the development of unique characterization methods for these USNPs. Last is a discussion of several novel applications of USNPs in biomedical imaging, catalysis, and semiconductor development, all of which benefit from the large surface-to-volume ratio and/or other characteristic properties inherent in USNPs.